Fixing apparatus and image forming apparatus

Abstract

Ensure the surface of the pressure roller is thoroughly discharged of static electricity. [Solution] The pressure roller 31 has a conductive surface layer 34 formed on the main part 31a of the roller so as to contact the surface of the fixing belt 21 at the nip portion, and a conductive, grounded annular member 65 is installed on the core metal 32 of the pressure roller 31 so as to face the end face of the main part 31a of the roller. The end face of the main part 31a of the roller is inclined so as to approach the annular member 65 from the roller surface side toward the roller center axis side when viewed in a cross-section including the roller center axis W of the pressure roller 31. In addition, the conductive surface layer 34 has a folded portion 34a formed at the widthwise end on the side where the annular member 65 is installed, which is folded in from the roller surface side toward the roller center axis side along the inclination of the end face of the main part 31a of the roller. The folded portion 34a is in contact with the end face of the annular member 65.

Description

Technical Field

[0001] The present invention relates to a fixing device that heats and fixes a toner image carried on the surface of a sheet, and an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine equipped with the same.

Background Art

[0002] Conventionally, in a fixing device installed in an image forming apparatus such as a copying machine or a printer, a technique for discharging a pressure roller is known in order to prevent the occurrence of abnormal images such as electrostatic offset (see, for example, Patent Document 1).

[0003] On the other hand, Patent Document 1 discloses a technique of installing an annular conductive elastic member for discharging a fixing belt or a pressure roller on a shaft portion at a widthwise end of the pressure roller.

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the conventional fixing device, the surface of the pressure roller was not sufficiently discharged, and the occurrence of abnormal images such as electrostatic offset could not be sufficiently reduced.

[0005] The present invention has been made to solve the above problems, and an object thereof is to provide a fixing device and an image forming apparatus capable of sufficiently discharging the surface of a pressure roller.

Means for Solving the Problems

[0006] The fixing device in this invention comprises a fixing rotating body heated by a heat source, and a pressure roller that forms a nip portion on which a sheet is conveyed by pressing it against the fixing rotating body. The pressure roller comprises a conductive surface layer formed on the main part of the roller so as to contact the surface of the fixing rotating body at the nip portion, and a conductive, grounded annular member installed on the shaft of the pressure roller so as to face the end face of the main part of the roller. The end face of the main part of the roller is inclined so as to approach the annular member from the roller surface side toward the roller central axis side when viewed in a cross-section including the roller central axis of the pressure roller. The conductive surface layer has a folded portion at the widthwise end on the side where the annular member is installed, which is folded in from the roller surface side toward the roller central axis side along the inclination of the end face of the main part of the roller, and the folded portion is in contact with the end face of the annular member. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a fixing device and an image forming apparatus that can sufficiently remove static electricity from the surface of a pressure roller. [Brief explanation of the drawing]

[0008] [Figure 1] This is an overall configuration diagram showing an image forming apparatus according to an embodiment of the present invention. [Figure 2] This is a diagram showing the configuration of the fixing device. [Figure 3] This is a top view of the fixing device as seen in the width direction. [Figure 4] This is a schematic side view showing the anchoring belt and guide member in the width direction. [Figure 5] This is a cross-sectional view showing a fixing device connected to the earth path. [Figure 6] This is a cross-sectional view showing the widthwise end of the main part of the fixing device. [Figure 7] This is a cross-sectional view showing the widthwise end of the main part of the fixing device, as an example of a comparative example. [Figure 8]This figure shows the relationship between the knurling diameter of the annular member and the outer diameter of the end of the pressure roller, as an example of modified example 1. [Figure 9] This is a cross-sectional view showing the widthwise end of the main part of the fixing device, as a modified example 2. [Figure 10] This is a cross-sectional view showing the widthwise end of the main part of the fixing device, as a modified example 3. [Figure 11] This is a cross-sectional view showing the widthwise end of the main part of the fixing device, as an example of a comparative example. [Modes for carrying out the invention]

[0009] Hereinafter, embodiments for carrying out this invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and redundant explanations will be simplified or omitted as appropriate.

[0010] First, Figure 1 will explain the overall configuration and operation of the image forming apparatus 100. In Figure 1, 100 represents a small printer as an image forming apparatus, 1 represents a photosensitive drum on which a toner image is formed, 6 represents a process cartridge that integrates the photosensitive drum 1, a charging roller 4, a developing device 5, and a cleaning device 2, and 7 represents an exposure device (writing unit) that irradiates the photosensitive drum 1 with exposure light L based on image information input from an input device such as a personal computer. Furthermore, 9 is a transfer roller that transfers the toner image supported on the surface of the photoreceptor drum 1 to the sheet P which is transported to the transfer nip section (transfer position), 12 is a paper feed device (paper feed cassette) in which the sheet P such as paper is stored, 16 is a register roller (timing roller) that transports the sheet P toward the transfer nip section where the photoreceptor drum 1 and the transfer roller 9 come into contact, and 20 is a fixing device that fixes the unfixed image on the sheet P.

[0011] Here, a charging roller 4, a developing device 5, a cleaning device 2, and other components are arranged around the photoreceptor drum 1. These components (photoreceptor drum 1, charging roller 4, developing device 5, and cleaning device 2) are integrated as a process cartridge 6 and are installed in a detachable (replaceable) manner on the image forming apparatus body 100 (apparatus body). The process cartridge 6 is mainly removed from the image forming apparatus body 100 by the user and replaced with a new one when it reaches a predetermined replacement cycle.

[0012] Referring to Figure 1, the operation of the image forming apparatus 100 during normal image forming will be described. First, when image information is transmitted from an input device such as a personal computer to the exposure device 7 of the image forming apparatus 100, the exposure device 7 emits exposure light L (laser light) based on that image information toward the surface of the photoreceptor drum 1. Meanwhile, the photoreceptor drum 1 is driven by a drive motor installed in the image forming apparatus body 100 and rotates in the direction of the arrow (clockwise). First, the surface of the photoreceptor drum 1 is uniformly charged at the position opposite the charging roller 4 (this is the charging process). In this way, a charge potential (approximately -900V) is formed on the photoreceptor drum 1. Subsequently, the charged surface of the photoreceptor drum 1 reaches the irradiation position of the exposure light L. Then, the potential of the part irradiated by the exposure light L becomes the latent image potential (approximately 0 to -100V), and an electrostatic latent image is formed on the surface of the photoreceptor drum 1 (this is the exposure process).

[0013] Subsequently, the surface of the photoreceptor drum 1, on which the electrostatic latent image has formed, reaches a position opposite the developing device 5. Then, toner is supplied from the developing device 5 onto the photoreceptor drum 1, and the latent image on the photoreceptor drum 1 is developed to form a toner image (this is the developing process). After that, the surface of the photoreceptor drum 1 after the developing process reaches the transfer nip portion (transfer position) with the transfer roller 9. Then, at the transfer nip portion with the transfer roller 9, a transfer bias (a bias having a polarity different from the polarity of the toner) is applied from the power supply unit to the transfer roller 9, and the toner image formed on the photoreceptor drum 1 is transferred onto the sheet P conveyed by the resist roller 16 (this is the transfer process).

[0014] Then, the surface of the photoreceptor drum 1 after the transfer process reaches the position facing the cleaning device 2. And at this position, the untransferred toner remaining on the photoreceptor drum 1 is mechanically removed by the cleaning blade and recovered into the cleaning device 2 (this is the cleaning process). Thus, a series of image forming processes on the photoreceptor drum 1 is completed.

[0015] On the other hand, the sheet P conveyed to the transfer nip portion between the photoreceptor drum 1 and the transfer roller 9 operates as follows. First, the uppermost sheet P stored in the paper feeding device 12 is fed by the paper feeding roller 15 toward the conveyance path. After that, the sheet P reaches the position of the resist roller 16. And the sheet P that has reached the position of the resist roller 16 is conveyed toward the transfer nip portion (the contact position between the transfer roller 9 and the photoreceptor drum 1) while synchronizing the timing to align with the image formed on the photoreceptor drum 1.

[0016] After passing through the position of the transfer nip portion (transfer roller 9), the sheet P after the transfer process reaches the fixing device 20 through the conveyance path. The sheet P that has reached the fixing device 20 is fed between the fixing belt 21 and the pressure roller 31, and the image is fixed by the heat received from the fixing belt 21 and the pressure received from both members 21 and 22 (this is the fixing process). The sheet P on which the image has been fixed is discharged from between the fixing belt 21 and the pressure roller 31 (the fixing nip) and then discharged from the image forming apparatus main body 100 and placed on the paper discharge tray. In this way, a series of image forming processes is completed.

[0017] Next, the configuration and operation of the fixing device 20 will be described using FIGS. 2 to 6 and the like. The fixing device 20 is a device that conveys the sheet P (a sheet carrying unfixed toner) while heating it. Referring to FIG. 2 and the like, the fixing device 20 includes a fixing belt 21 as a fixing rotating body, a planar heater 24 as a heat source (heating means), a holder 23, a stay 30, a thermistor 40, a pressure roller 31 as a pressurizing rotating body, an annular member 65 (see FIGS. 3, 5, 6, etc.), and the like.

[0018] Here, the fixing belt 21 is an endless belt member that is externally circumscribed to the pressure roller 31 and rotates passively as the pressure roller 31 rotates. The fixing belt 21 is a thin and flexible endless belt, and rotates (passively rotates) in the direction of the arrow (clockwise direction) in FIG. 2. Referring to FIG. 5 (not to scale) and the like, the fixing belt 21 has a base material layer 21a as a belt conductive layer and an insulating (or medium resistance) belt surface layer 21b (surface layer) laminated from the inner peripheral surface (the surface in sliding contact with the planar heater 24), and the overall thickness is set to 1 mm or less. The base material layer 21a of the fixing belt 21 has a layer thickness of 30 to 50 μm, and is formed of a metal material such as nickel or stainless steel, or a material in which carbon is dispersed in a resin material such as polyimide, and functions as a belt conductive layer having conductivity. The belt surface layer 21b of the fixing belt 21 has a layer thickness of 5 to 50 μm, and is formed of an insulating material such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), polyimide, polyetherimide, PES (polyethersulfone), or the like. By providing the insulating belt surface layer 21b, the releasability (peelability) with respect to the toner (toner image) is ensured. In addition, in this embodiment, the belt surface layer 21b is formed of an insulating material, but it can also be formed of a medium resistance material by dispersing a relatively small amount of carbon in the above-described insulating material.

[0019] On the inside (inner circumferential surface) of the fixing belt 21, a planar heater 24, a holder 23, a stay 30, a thermistor 40, etc., are installed. Here, the planar heater 24 is positioned to extend in the width direction (the direction perpendicular to the plane of the paper in Figure 2, the left-right direction in Figures 3 to 6, and synonymous with the "axial direction"). The planar heater 24 presses against the pressure roller 31 via the fixing belt 21 on the inside (inner circumferential surface side) of the fixing belt 21, forming a nip section (fixing nip) through which the sheet P is conveyed. In other words, the planar heater 24 is installed so as to slide against the inner circumferential surface of the fixing belt 21. The planar heater 24 presses against the pressure roller 31 via the fixing belt 21, thereby forming a nip section through which the sheet P is conveyed. In this way, the planar heater 24 functions as a member that forms a nip section (fixing nip) (nip section forming member). Furthermore, the planar heater 24 has a resistive pattern (heat-generating resistor) formed on the portion that slides against the inner circumferential surface of the fixing belt 21. Power is supplied to the resistive pattern from a power supply unit (not shown), and the resistive pattern generates heat due to its resistance, thereby heating the fixing belt 21. In this way, the planar heater 24 also functions as a heat source (heating means) for heating the fixing belt 21.

[0020] Furthermore, in this embodiment, in order to reduce the sliding resistance between the planar heater 24 and the inner surface of the fixing belt 21, a lubricant such as silicone oil or fluorine grease is directly applied to the inner surface of the fixing belt 21. In this embodiment, the lubricant was directly applied to the inner circumferential surface of the fixing belt 21. However, the lubricant can also be applied indirectly to the inner circumferential surface of the fixing belt 21 by applying the lubricant to the sliding contact surface of the planar heater 24, for example. In addition to applying lubricant to the inner surface of the fixing belt 21, the surface of the planar heater 24 can also be covered with a sheet-like member made of a low-friction material such as PTFE or a surface layer can be provided.

[0021] In this embodiment, the planar heater 24 is held by the holder 23 (holding member). The holder 23 has a recess formed therein, into which the planar heater 24 is fitted, thereby holding the planar heater 24 across its width. The holder 23 is held by the stay 30 while holding the planar heater 24. The stay 30, which holds the planar heater 24 and the holder 23, is held by the frame 60 of the fixing device 20 at both ends in the width direction via flange members 42 (see Figure 3, etc.).

[0022] In this way, the fuser belt 21 is directly heated by a planar heater 24 (resistor pattern) installed inside it. Then, heat is applied to the toner image on the sheet P from the surface of the heated fuser belt 21. Here, the output control of the planar heater 24 is performed based on the temperature detection result by the thermistor 40, which is in direct (or indirectly via another component) contact with the planar heater 24. In this embodiment, there is no temperature sensor that directly detects the surface temperature of the fixing belt 21. Instead, the temperature of the planar heater 24 is controlled by the thermistor 40, thereby indirectly controlling the surface temperature (fixing temperature) of the fixing belt 21 to reach a desired temperature.

[0023] Referring to Figure 4, the pair of flange members 42 guide both ends of the fixing belt 21 in the width direction from the inner circumferential surface side so that the fixing belt 21 maintains a substantially cylindrical position. More specifically, the two flange members 42 are made of a heat-resistant resin material or the like, and are held at both ends in the width direction of the frame 60 of the fixing device 20 so as to be slidable in the direction of forming a nip portion (fixing nip). The flange members 42 are provided with a guide portion 42a for holding the fixing belt 21 while maintaining the substantially cylindrical posture of the fixing belt 21, and a stopper portion for restricting the movement of the fixing belt 21 in the width direction (towards the belt), etc. Furthermore, in this embodiment, as shown in Figure 3, the fixing belt 21 (and the planar heater 24 and holder 23) are configured to be pressed against the pressure roller 31 by pressure applied by the pressure lever 52 (pressure mechanism 51) via the flange member 42. Furthermore, the flange members 42 are positioned at both ends in the width direction, within the circumferential range excluding the fixing nip, so as not to interfere with the formation of the fixing nip by the planar heater 24. Furthermore, in this embodiment, the only members that contact the inner circumferential surface of the fixing belt 21 are the flange members 42 that make loose contact at both ends in the width direction and the planar heater 24, and there are no other members (belt guides) that contact the inner circumferential surface and guide the rotation of the fixing belt 21.

[0024] In this embodiment, the stay 30 is installed inside the fixing belt 21 so as to contact the pressure roller 31 via the planar heater 24 (and holder 23) and the fixing belt 21. The stay 30 reinforces the strength of the planar heater 24 (and holder 23) that forms the fixing nip, and is installed on the frame 60 (or holder 23) by screw fastening or the like. Furthermore, the stay 30 contacts the pressure roller 31 via the planar heater 24 (and holder 23) and the fixing belt 21, thereby preventing the planar heater 24 (and holder 23) from deforming significantly in the fixing nip due to the pressure applied by the pressure roller 31. In order to satisfy the above-mentioned function, it is preferable that the stay 30 be made of a metal material with high mechanical strength, such as stainless steel or iron.

[0025] While resin materials and metal materials can be used to form the holder 23, a resin material (such as liquid crystal polymer (LCP), polyamide-imide (PAI), polyethersulfone (PES), polyphenylene sulfide (PPS), polyethernitrile (PEN), polyetheretherketone (PEEK), etc.) is preferred as it has sufficient rigidity to prevent excessive deflection even under pressure from the pressure roller 31, and possesses thermal and heat insulating properties. In this embodiment, liquid crystal polymer (LCP) is used as the material for the holder 23.

[0026] Referring to Figure 2, the pressure roller 31, which acts as a pressurizing rotating body, has an elastic layer 33 and a conductive surface layer 34 sequentially laminated on a core metal 32 which acts as a shaft, and is driven to rotate in a predetermined direction (counterclockwise in Figure 2) by a drive motor 95. The core metal 32 (shaft portion) of the pressure roller 31 is a hollow structure made of a metal material (conductive material). The elastic layer 33 of the pressure roller 31 is made of an insulating material such as foamed silicone rubber, silicone rubber, or fluororubber. The conductive surface layer 34 of the pressure roller 31 is a thin surface layer (release layer) formed by dispersing carbon or the like in PFA, PTFE, etc., and is electrically conductive. In this embodiment, the conductive surface layer 34 is tubular and can be formed by covering the elastic layer 33 with a tube and subjecting it to heat processing or the like. The conductive surface layer 34 will be explained in more detail later with reference to Figure 6, etc. The pressure roller 31 presses against the fixing belt 21 to form a desired nip (fixing nip) between the two components. Also, referring to Figure 3, a gear 45 that meshes with the drive gear of the drive motor is installed on the pressure roller 31, and the pressure roller 31 is rotated in the direction of the arrow in Figure 2 (counterclockwise). Furthermore, both ends of the pressure roller 31 in the width direction are rotatably supported on the frame 60 of the fixing device 20 via bearings. In this embodiment, the fixing device 20 is also equipped with an annular member 65, which will be explained in detail later.

[0027] The following briefly describes the normal operation of the fixing device 20 configured as described above. When a print command is input to the main unit 100, power is supplied to the planar heater 24, and the drive motor 95 starts rotating the pressure roller 31 in the direction of the arrow in Figure 2. As a result, the fixing belt 21 also rotates in the direction of the arrow in Figure 2 due to the frictional force between the fixing nip and the pressure roller 31. Subsequently, the sheet P is fed from the paper feeder 12, and the unfixed image is placed (transferred) onto the sheet P at the position of the transfer roller 9. The sheet P, on which the unfixed image (toner image) is placed, is guided by an entrance guide plate (not shown) and transported in the direction of arrow Y10 in Figure 2, and is fed into the nip section (fixing nip) of the fixing belt 21 and pressure roller 31, which are in a pressed state. Then, the toner image is fixed to the surface of the sheet P by heating from the fixing belt 21 heated by the planar heater 24, and by the pressing force between the planar heater 24 (and holder 23), reinforced by the stay 30, and the pressure roller 31. After that, the sheet P, which has been fed out from the fixing nip, is transported in the direction of arrow Y11 while being guided by an exit guide plate (not shown).

[0028] The configuration and operation of the characteristic fixing device 20 in the image forming apparatus 100 of this embodiment will be described in detail below. As explained earlier using Figures 2 and 5, the fixing belt 21 is provided with a base layer 21a, which serves as a conductive belt layer. In addition, an insulating belt surface layer 21b (or a belt surface layer with medium resistance) is directly laminated onto the base layer 21a (belt conductive layer) of the fixing belt 21. In other words, the fixing belt 21 in this embodiment has a two-layer structure in which a conductive belt conductive layer is used as a base layer 21a, and an insulating or medium-resistance belt surface layer 21b is laminated on the base layer 21a.

[0029] In particular, in this embodiment, one end of the base material layer 21a (belt conductive layer) in the width direction (the side on which the conductive annular member 65, described later, is installed, which is the left side in Figure 5) is formed to protrude beyond the belt surface layer 21b in the width direction. That is, the base material layer 21a (conductive belt conductive layer) has a portion that is exposed at the width direction end on the side on which the annular member 65 is installed. Then, the base material layer 21a (belt conductive layer) that protrudes from one end in the width direction comes into direct contact with the annular member 65, which will be described later (a contact portion is formed). Therefore, the belt surface layer 21b is laminated on the base layer 21a (belt conductive layer) in the width direction (left-right direction in Figures 5 and 6, and axial direction) excluding the contact area between the base layer 21a and the annular member 65 described later. In other words, the belt surface layer 21b is directly laminated on the base layer 21a in the width direction excluding the exposed portion of the base layer 21a.

[0030] On the other hand, the pressure roller 31, which acts as a pressurizing rotating body, is provided with a conductive surface layer 34 (which has conductivity) that contacts the belt surface layer 21b of the fixing belt 21 (fixing rotating body) to form a nip portion (fixing nip). The conductive surface layer 34 is formed on the main part of the roller 31a (the part in which the elastic layer 33 and the conductive surface layer 34 are laminated) so as to contact the surface of the fixing belt 21 at the nip portion. Here, as shown in Figures 5 and 6, the pressure roller 31 (pressure rotating body) of the fixing device 20 in this embodiment has a conductive, grounded annular member 65 installed on the core metal 32, which is the shaft portion of the pressure roller 31, so as to face the end face of the roller main portion 31a (the portion in which the elastic layer 33 and conductive surface layer 34 are formed, excluding the ends where only the core metal 32 is exposed). Furthermore, the annular member 65 in this embodiment is in contact with and electrically connected to the exposed portion of the base material layer 21a (belt conductive layer) (the portion where the belt surface layer 21b is not laminated and is exposed on one end in the width direction). Therefore, the annular member 65 is in contact with and electrically connected to the base material layer 21a (belt conductive layer) and the conductive surface layer 34 of the fixing belt 21, respectively.

[0031] More specifically, as shown in Figures 5 and 6, the annular member 65 is an annular (donut-shaped) member made of a conductive material. In particular, the annular member 65 in this embodiment has knurling (multiple bumps and grooves) formed on its outer circumferential surface, and this outer circumferential surface is in contact with the exposed portion of the base material layer 21a (belt conductive layer). The annular member 65 functions as a conductive member for grounding the base layer 21a (belt conductive layer) and the conductive surface layer 34 of the fixing belt 21, respectively.

[0032] The annular member 65 is inserted (installed) into the core metal 32 of the pressure roller 31 (which functions as the shaft at the end) so as to contact the base material layer 21a (belt conductive layer) of the fixing belt 21 and the end face of the main roller portion 31a of the pressure roller 31. The annular member 65 then rotates together with the pressure roller 31 in a predetermined direction (counterclockwise in Figure 2).

[0033] Furthermore, in this embodiment, the outer diameter (knurled outer diameter) of the annular member 65 is approximately equal to or slightly larger than the outer diameter of the main roller portion 31a of the pressure roller 31 (the portion on which the elastic layer 33 and conductive surface layer 34 are formed). The knurled protrusions of the annular member 65 are in contact with the base material layer 21a of the fixing belt 21 (the exposed portion of the belt conductive layer). In this case, even if the outer diameter of the annular member 65 (knurled outer diameter) is the same as the outer diameter of the main roller portion 31a, the belt surface layer 21b is extremely thin, and the pressure roller 31 presses against the fixing belt 21 in a way that it bites into it, so the annular member 65 (protrusion) comes into contact with the base material layer 21a (belt conductive layer) and becomes electrically conductive. In this embodiment, a knurled member with multiple bumps and grooves on its outer surface (in this embodiment, a spur gear shape) is used as the annular member that contacts the base material layer 21a (belt conductive layer) of the fixing belt 21. Therefore, compared to the case where a completely annular member is in contact with the base material layer 21a, multiple protrusions arranged in the circumferential and width directions alternately contact the base material layer 21a, reducing contact defects such as uneven contact, and as a result, it becomes possible to ensure good, stable, and relatively large contact pressure for electrical conductivity with the base material layer 21a.

[0034] In this embodiment, the annular member 65 is press-fitted onto the core metal 32 to enhance conductivity (electrical connectivity) with the core metal 32, which serves as the shaft. Furthermore, to prevent misalignment of the annular member 65 in the width direction (axial direction) of the core metal 32, the annular member 65 can also be bonded and fixed to the core metal 32 via a conductive adhesive. Furthermore, as shown in Figure 5, in this embodiment, the annular member 65 is grounded via the core metal 32. More specifically, the core metal 32 is connected to the grounding wire (connected to the grounded frame 60) on which the resistor 68 (electrical resistance component) is installed. As a result, the annular component 65 is properly grounded. Furthermore, the annular member 65 is positioned outside the maximum paper-feeding area M of the fixing device 20 (the widthwise range through which the largest possible sheet P can be transported passes) (non-paper-feeding area). As a result, there is no influence from the annular member 65 coming into contact with the fixed image.

[0035] As described above, the fixing device 20 in this embodiment is equipped with an annular member 65 that functions as a conductive member, thereby ensuring good electrical conductivity between the base layer 21a (belt conductive layer) of the fixing belt 21 and the conductive surface layer 34 of the pressure roller 31 and the grounded annular member 65. Consequently, charge is less likely to accumulate on the fixing belt 21 and the pressure roller 31, reducing the occurrence of abnormal images such as electrostatic offset due to charge accumulation.

[0036] "Electrostatic offset" is a phenomenon that occurs during the fixing process when toner carried on the sheet P fed into the nip section (fixing nip) electrostatically transfers to and adheres to the surface of the fixing belt 21 (fixing rotating body), and this adhered toner then reattaches to the sheet P as the fixing belt 21 completes one rotation. This transfer of toner to the fuser belt 21 occurs because the surfaces of the fuser belt 21 and the pressure roller 31 each become electrically charged. In particular, the toner used in this embodiment has a negative polarity, and when the fuser belt 21 becomes positively charged and the pressure roller 31 becomes negatively charged, the toner receives an electrostatic repulsive force from the pressure roller 31 side and an electrostatic adsorption force from the fuser belt 21 side, causing it to adhere to the fuser belt 21. In response to this phenomenon, as described above, the fixing device 20 in this embodiment actively removes static electricity from the base layer 21a (belt conductive layer) of the fixing belt 21 and the conductive surface layer 34 of the pressure roller 31, so that the surfaces of the fixing belt 21 and the pressure roller 31 are less likely to become charged. Therefore, electrostatic offset is less likely to occur.

[0037] Referring to Figure 6, etc., the end face of the main roller portion 31a of the pressure roller 31 (the end face on the side of the annular member 65) is inclined (formed in a tapered shape) so as to approach the annular member 65 from the roller surface side towards the roller central axis side when viewed in a cross-section including the roller central axis W of the pressure roller 31 (when viewed in a cross-section including the roller central axis W that extends in the axial direction). In other words, the main roller portion 31a is formed such that the outer diameter at one end in the width direction is smaller than the outer diameter of the rest of the portion (referred to as "the outer diameter of the pressure roller" as appropriate). To put it another way, the end of the main roller portion 31a at one end in the width direction is formed in a roughly frustoconical shape. Note that the shape of these roller main parts 31a is that of the roller main part 31 when it is not thermally expanded and is at room temperature.

[0038] Referring to Figure 6, etc., in the pressure roller 31 of this embodiment, the conductive surface layer 34 has a folded portion 34a formed at the widthwise end (one end in the widthwise direction, which is the left end in Figures 5 and 6) on the side where the annular member 65 is installed. This folded portion 34a is a portion that is folded from the roller surface side (the side of the outer diameter (circumferential surface) of the pressure roller 31) toward the roller central axis side (the side of the roller central axis W) so as to follow the inclination of the end face of the roller main portion 31a of the pressure roller 31 (the part on which the elastic layer 33 and the conductive surface layer 34 are formed) (including cases where it is formed to appear folded in appearance even if it is not actually folded in the manufacturing process). In particular, the conductive surface layer 34 in this embodiment is tubular in shape and is formed to cover almost the entire area of ​​the outer circumferential surface and end face of the elastic layer 33. Furthermore, the folded portion 34a is configured to contact the end face of the annular member 65. That is, the conductive surface layer 34 is folded in at an inclination so that its widthwise end (axial end) follows the inclined end face of the elastic layer 33, and its tip portion 34a1 (the small diameter portion near the core metal 32) contacts the end face of the annular member 65.

[0039] In this way, by bringing the tip portion 34a1 (small diameter portion) of the folded portion 34a formed on the conductive surface layer 34 along the inclination (tapered shape) on one end in the width direction of the main roller portion 31a (elastic layer 33) into contact with the end face of the annular member 65, even if the pressure roller 31 expands due to heat during the fixing process (actual use) and the shape of the end face deforms, poor contact (poor conductivity) between the folded portion 34a and the end face of the annular member 65 becomes less likely to occur. In other words, as shown in Figure 7 as a comparative example, in the case of the pressure roller 131, where the end face of the roller main part (elastic layer 133) is a plane substantially perpendicular to the roller central axis W, and the folded portion 134a of the conductive surface layer 134 is formed along this substantially perpendicular end face, the pressure roller 31 expands due to heat during the fixing process (actual use), causing deformation of the end face, which makes poor contact (poor conductivity) between the folded portion 34a and the end face of the annular member 65 more likely. In particular, the inner diameter portion of the pressure roller 31 (roller main part 31a), which is bonded (joined) to the core metal 32, is less prone to thermal expansion, while the outer diameter portion, which is not restricted by such bonding, expands easily in the direction of the white arrow in Figure 7. When such thermal expansion occurs, the annular member 65 deforms as if being pressed by the roller main part 31a, which makes poor contact (poor conductivity) between the folded portion 34a and the end face of the annular member 65 more likely. In contrast, in this embodiment, anticipating the thermal expansion of the pressure roller 31 (roller main portion 31a) during the fixing process (actual use) as described with reference to Figure 7, the end on one side in the width direction of the pressure roller 31 (roller main portion 31a) is formed in a substantially frustoconical shape, and the folded portion 34a is formed to conform to the shape of that end face. As a result, poor contact (poor conductivity) between the folded portion 34a and the end face of the annular member 65 is less likely to occur. Rather, when the roller main portion 31a expands due to heat during the fixing process (actual use), the outer diameter side of the folded portion 34a, as well as the inner diameter side, is more likely to come into contact with the end face of the annular member 65, ensuring a sufficient contact area between the conductive surface layer 34 and the annular member 65. Therefore, the surface of the pressure roller 31 (conductive surface layer 34) is sufficiently discharged, and the occurrence of abnormal images such as electrostatic offset is sufficiently reduced.

[0040] <Example 1> Referring to Figure 8, the annular member 65 installed in the fixing device 20 in modified example 1 also has knurling formed on its outer surface, similar to that shown in Figure 6, and this knurled outer surface contacts the exposed portion of the base material layer 21a (belt conductive layer) of the fixing belt 21, thereby providing electrical contact. Here, the fixing device 20 shown in Figure 8(A) is configured such that the outer diameter D of the widthwise end of the roller main portion 31a (see Figure 5) on the side where the annular member 65 is installed (this is the outer diameter of the tip portion 34a1 (small diameter portion)) is smaller than the knurled inner diameter B1 of the annular member 65 (this is the diameter of the bottom of the knurled recess) (D <B1)。 In this configuration, the tip portion 34a1 (small diameter portion) of the conductive surface layer 34 (roller main portion 31a) abuts against the end face within the knurled inner diameter B1 of the annular member 65, thereby ensuring a sufficient contact area between the conductive surface layer 34 and the annular member 65. In contrast, the fixing device 20 shown in Figure 8(B) is configured such that the outer diameter D of the widthwise end of the roller main portion 31a on the side where the annular member 65 is installed (this is the outer diameter of the tip portion 34a1 (small diameter portion)) is larger than the knurled inner diameter B1 of the annular member 65 (this is the diameter of the bottom of the knurled recess) and smaller than the knurled outer diameter B2 of the annular member 65 (this is the diameter of the bottom of the knurled recess) (B1 <D<B2)。 In this configuration, the tip portion 34a1 (small diameter portion) of the conductive surface layer 34 (roller main portion 31a) abuts against the sides of the multiple protrusions of the knurling on the annular member 65. As a result, the multiple protrusions, which are arranged in a circumferential direction, alternately contact the base material layer 21a, reducing contact problems such as uneven contact, and consequently ensuring good, stable, and relatively large contact pressure for electrical conductivity with the base material layer 21a. Furthermore, in the fixing device 20 of the modified example 1, the surface of the pressure roller 31 can be sufficiently electrostatically discharged.

[0041] <Modification 2> As shown in Figure 9, in the fixing device 20 of the modified example 2, the annular member 65 has knurling formed on the end face facing the main roller portion 31a (see Figure 5). Furthermore, in the modified example 2, the fixing device 20 is also formed in the same way as in Figure 6, with the end of one end of the pressure roller 31 (roller main part 31a) in the width direction formed in a substantially frustoconical shape, and the folded portion 34a formed to conform to the shape of the end face. By forming the end face of the annular member 65 in a knurled shape in this way, the multiple protrusions arranged separately on the end face come into contact with the folded portion 34a, reducing poor contact such as uneven contact. As a result, it becomes possible to ensure good, stable, and relatively large contact pressure for electrical conductivity with the folded portion 34a (conductive surface layer 34). Furthermore, in the fixing device 20 of the modified example 2, the surface of the pressure roller 31 can also be sufficiently electrostatically discharged.

[0042] <Variation 3> As shown in Figure 10(A), in the fixing device 20 of modified example 3, the annular member 65 has multiple protrusions 65s formed on the outer circumferential side of the end face facing the main roller portion 31a, divided in the circumferential direction (or, one protrusion 65s is formed circumferentially). In contrast, the annular member 65 shown in Figure 10(B) has multiple recesses 65t formed on the inner circumferential side of the end face facing the main roller portion 31a (see Figure 5), divided in the circumferential direction (or, one recess 65t is formed circumferentially). Furthermore, both the annular member 65 shown in 10(A) and the annular member 65 shown in 10(B) have their outer circumferential surfaces in contact with the folded portion 34a, which is folded along the inclination of the end face of the roller main portion 31a. This configuration reduces poor contact (poor conductivity) between the folded portion 34a and the end face of the annular member 65. In other words, as shown in Figure 11 as a comparative example, if no protrusions 65s or recesses 65t are formed on the end face of the annular member 65, the elastic layer 33 of the pressure roller 31 expands axially due to the nip portion (fixing nip) and Poisson's ratio. If the annular member 65 deforms (collapses) due to this expansion, poor contact (poor conductivity) between the folded portion 34a and the end face of the annular member 65 is likely to occur. In contrast, in the modified example 3, anticipating deformation (tilting) of the annular member 65 as shown in Figure 11, a convex portion 65s and a concave portion 65t are formed on the end face of the annular member 65 so that contact with the folded portion 34a is maintained even if such deformation occurs, thus making the above-mentioned problems less likely to occur. Furthermore, in the fixing device 20 of the modified example 3, the surface of the pressure roller 31 can also be sufficiently electrostatically discharged.

[0043] As described above, the fixing device 20 in this embodiment includes a fixing belt 21 (fixing rotating body) heated by a planar heater 24 (heat source), and a pressure roller 31 that forms a nip portion on which the sheet P is conveyed by pressing it against the fixing belt 21. The pressure roller 31 has a conductive surface layer 34 formed on the main part 31a of the roller so as to contact the surface of the fixing belt 21 at the nip portion, and a conductive, grounded annular member 65 is installed on the core metal 32 (shaft portion) of the pressure roller 31 so as to face the end face of the main part 31a of the roller. The end face of the main part 31a of the roller is inclined so as to approach the annular member 65 from the roller surface side toward the roller center axis side when viewed in a cross-section including the roller center axis W of the pressure roller 31. Furthermore, the conductive surface layer 34 has a folded portion 34a formed at the widthwise end on the side where the annular member 65 is installed, which is folded in from the roller surface side toward the roller center axis side along the inclination of the end face of the main part 31a of the roller. Furthermore, the folded portion 34a is in contact with the end face of the annular member 65. This allows the surface of the pressure roller 31 to be sufficiently electrostatically discharged.

[0044] In this embodiment, the present invention was applied to a fixing device 20 using a planar heater 24 as a heat source. However, the fixing device to which the present invention is applied is not limited to this, and the present invention can naturally be applied to fixing devices using heaters or electromagnetic induction coils as heat sources, for example. Furthermore, in this embodiment, the present invention was applied to a fixing device 20 using a fixing belt 21 as the fixing rotating body. However, the fixing device to which the present invention is applied is not limited to this, and the present invention can naturally be applied to fixing devices such as fixing rollers or fixing belts (stretched between multiple roller members) as the fixing rotating body. Furthermore, in this embodiment, a base layer 21a was used as the belt conductive layer formed on the fixing belt 21. However, in the fixing belt 21, a conductive elastic layer and a belt surface layer 21b can be sequentially laminated on the base layer 21a (as a three-layer structure), and the conductive elastic layer can be used as the belt conductive layer. Furthermore, in this embodiment, an annular member 65 with knurling on its outer surface was used, but the outer surface of the annular member does not necessarily have to be knurled; for example, a gear-shaped annular member can also be used. Furthermore, in this embodiment, the planar heater 24, which serves as a heat source, is configured to form a nip portion (fixed nip) by being pressed against the pressure roller 31 via the fixing belt 21 as a nip-forming member. However, the nip-forming member does not necessarily have to be a heat source. Furthermore, in this embodiment, the annular member 65 is configured to form an earth path by contacting the folded portion 34a (pressure roller 31) and the base material layer 21a (fixing belt 21), respectively. However, it is also possible to form an earth path by contacting only the folded portion 34a (pressure roller 31) with the annular member 65, and to form a separate earth path with respect to the base material layer 21a (fixing belt 21). Furthermore, the same effects as those of this embodiment can be obtained in these cases as well.

[0045] It is clear that the present invention is not limited to this embodiment, and that this embodiment can be modified as appropriate within the scope of the technical concept of the present invention, in addition to what is suggested here. Furthermore, the number, position, shape, etc. of the constituent members are not limited to this embodiment, and can be set to a number, position, shape, etc. that is suitable for carrying out the present invention.

[0046] In this specification, the term "sheet" is defined to include not only paper but also all sheet-like recording media such as coated paper, label paper, OHP sheets, and film sheets that are transported. [Explanation of Symbols]

[0047] 20 Fixing device, 21 Fixing belt (fixing rotating body), 21a Substrate layer (belt conductive layer), 21b Belt surface layer, 24-sided heater (heat source), 31 Pressure roller (pressure rotating body), 31a Roller main section, 32 Core metal (shaft part), 33. Elastic layer (insulating elastic layer), 34 conductive surface layer, 34a Folded section, 34a1 Small diameter section, 65 circular annular member, 65s convex part, 65t recess, 68 Resistors (electrical resistance components), 100 Image forming apparatus (image forming apparatus main unit), W Roller central axis (rotational central axis), P-sheet (recording medium).

[0048] Furthermore, the embodiments of the present invention can also be, for example, combinations of appendices 1 to 8 as follows. (Note 1) A fixing rotating body heated by a heat source, A pressure roller that forms a nip section on which the sheet is conveyed by pressing it against the aforementioned fixing rotating body, Equipped with, The aforementioned pressure roller A conductive surface layer is formed on the main part of the roller so as to contact the surface of the fixing rotating body at the nip portion, and the conductive surface layer is formed on the main part of the roller so as to contact the surface of the fixing rotating body at the nip portion, An annular member, which is conductive and grounded, is installed on the shaft portion of the pressure roller so as to face the end face of the main portion of the roller, It is equipped with, The end face of the main part of the roller is inclined such that, when viewed in a cross-section including the roller central axis of the pressure roller, it approaches the annular member from the roller surface side toward the roller central axis side. The conductive surface layer has a folded portion at the widthwise end on the side where the annular member is installed, which is folded in from the roller surface side toward the roller central axis side so as to follow the inclination of the end face of the main part of the roller. A fixing device characterized in that the folded portion contacts the end face of the annular member. (Note 2) The fixing belt of the aforementioned fixing rotating body, A portion is formed at the widthwise end of the side on which the annular member is installed, and a conductive belt conductive layer is formed thereon. An insulating or medium-resistance belt surface layer is directly or indirectly laminated on the belt conductive layer in the width direction, excluding the exposed portion, It is equipped with, The fixing device according to Appendix 1, characterized in that the annular member contacts and conducts electricity with the exposed portion of the belt conductive layer. (Note 3) The fixing device according to Appendix 2, characterized in that the annular member has knurling formed on its outer circumferential surface, and the outer circumferential surface contacts the exposed portion of the belt conductive layer. (Note 4) The fixing device according to Appendix 3, characterized in that the outer diameter of the widthwise end of the roller main portion on the side where the annular member is installed is smaller than the inner diameter of the knurling of the annular member. (Note 5) The fixing device according to Appendix 3, characterized in that the outer diameter of the widthwise end of the roller main portion on the side where the annular member is installed is larger than the knurled inner diameter of the annular member and smaller than the knurled outer diameter of the annular member. (Note 6) The fixing device according to any one of the appendices 1 to 5, characterized in that the annular member has knurling formed on the end face facing the main part of the roller. (Note 7) The annular member is, On the end face facing the main part of the roller, a convex portion is formed on the outer circumferential surface side, or a concave portion is formed on the inner circumferential surface side, The fixing device according to any one of the appendices 1 to 6, characterized in that its outer peripheral surface contacts the folded portion which is folded along the inclination of the end face of the main part of the roller. (Note 8) An image forming apparatus characterized by being equipped with a fixing device described in any of Appendix 1 to Appendix 7. [Prior art documents] [Patent Documents]

[0049] [Patent Document 1] Japanese Patent Publication No. 2018-13613

Claims

1. A fixing rotating body heated by a heat source, A pressure roller that forms a nip section on which the sheet is conveyed by pressing it against the aforementioned fixing rotating body, Equipped with, The aforementioned pressure roller A conductive surface layer is formed on the main part of the roller so as to contact the surface of the fixing rotating body at the nip portion, and the conductive surface layer is formed on the main part of the roller so as to contact the surface of the fixing rotating body at the nip portion, An annular member, which is conductive and grounded, is installed on the shaft portion of the pressure roller so as to face the end face of the main portion of the roller, It is equipped with, The end face of the main part of the roller is inclined such that, when viewed in a cross-section including the roller central axis of the pressure roller, it approaches the annular member from the roller surface side toward the roller central axis side. The conductive surface layer has a folded portion at the widthwise end on the side where the annular member is installed, which is folded in from the roller surface side toward the roller central axis side so as to follow the inclination of the end face of the main part of the roller. A fixing device characterized in that the folded portion contacts the end face of the annular member.

2. The fixing belt of the aforementioned fixing rotating body, A portion is formed at the widthwise end of the side on which the annular member is installed, and a conductive belt conductive layer is formed thereon. An insulating or medium-resistance belt surface layer is directly or indirectly laminated on the belt conductive layer in the width direction, excluding the exposed portion, It is equipped with, The fixing device according to claim 1, characterized in that the annular member contacts and conducts electricity with the exposed portion of the belt conductive layer.

3. The fixing device according to claim 2, characterized in that the annular member has knurling formed on its outer circumferential surface, and the outer circumferential surface contacts the exposed portion of the belt conductive layer.

4. The fixing device according to claim 3, characterized in that the outer diameter of the widthwise end of the roller main portion on the side where the annular member is installed is smaller than the inner diameter of the knurling of the annular member.

5. The fixing device according to claim 3, characterized in that the outer diameter of the widthwise end of the roller main portion on the side where the annular member is installed is larger than the knurled inner diameter of the annular member and smaller than the knurled outer diameter of the annular member.

6. The fixing device according to claim 1 or 2, characterized in that the annular member has knurling formed on the end face facing the main part of the roller.

7. The annular member is, On the end face facing the main part of the roller, a convex portion is formed on the outer circumferential surface side, or a concave portion is formed on the inner circumferential surface side, The fixing device according to claim 1 or 2, characterized in that its outer peripheral surface contacts the folded portion which is folded along the inclination of the end face of the main part of the roller.

8. An image forming apparatus characterized by comprising a fixing device according to claim 1 or claim 2.

Images